The potential of bunyaviruses for recombination and complementation will be studied in genetic and molecular analyses initially using prototype belonging to the California encephalitis subgroup of bunyaviruses. Later other viruses of the Bunyamwera supergroup will be examined in order to determine the recombination potential groupings of bunyaviruses (i.e., which bunyaviruses are able to recombine with each other). Temperature sensitive (ts) mutants of prototype viruses will be obtained from wild-type virus stocks and categorized into recombination and complementation groups using dual mutant virus infections. Using ts mutants of homologous alternate bunyaviruses isolates and later heterologous bunyaviruses (with distinguishable genome RNA oligonucleotide fingerprints and virion proteins) recombinants will be generated with mutants of the original prototypes in order to determine the mechanism of recombination and the coding function of each RNA segment. Recombinants generated between bunyaviruses in a Class III facility at Birmingham will, in continuance of our previous practices, be tested for pathogenicity before undertaking any molecular analyses. Pathogenicity studies, as well as serological analyses of surviving animals, will be undertaken by Dr. R.E. Shope in the consortium arrangement using a Class III animal facility at Yale University. The results of the pathogenicity studies will be reviewed by both Internal and External Peer review committees before any molecular analyses are undertaken in the Class III facility at Birmingham. Ts mutants of snowshoe hare virus will be used to study the mechanism of virus replication, protein synthesis an RNA transcription and replication. The question of how the viral proteins are synthesized and processed will be investigated by both conventional and genetic approaches. Bunyavirus preparations containing defective virus will be characterized in terms of their RNA composition and heterologous interference capabilities.